Pope Francis has lashed out at wealthy minorities who hoard resources at the expense of the poor during his visit to a crowded slum in Kenya's capital.

The 78-year-old pontiff was given a rapturous welcome as he arrived in Kangemi, which is home to more than 100,000 people who live in shacks without sewerage, including 20,000 who belong to the local Catholic parish.

"These are wounds inflicted by minorities who cling to power and wealth, who selfishly squander while a growing majority is forced to flee to abandoned, filthy and run-down peripheries," he told crowds in the slum on the outskirts of the capital.

[The lack of infrastructure and basic services] are a consequence of new forms of colonialism.

Pope Francis speaking in Kangemi

Wild singing and howling broke out as he arrived early on Friday, his pope-mobile weaving through streets in a sea of tin-roofed homes.

"I am here because I want you to know that I am not indifferent to your joys and hopes, your troubles and your sorrows," Pope Francis told the packed congregation in the church of St Joseph the Worker in Kangemi.

"I realise the difficulties which you experience daily. How can I not denounce the injustices which you suffer?"

People arrived long hours before dawn in the hope of catching a glimpse of the Pope, who has made efforts for social justice a hallmark of his tenure.

"It is once in a lifetime," said Edward Mwaniki, who comes from Kangemi and who waited for hours with his wife and three sons.

"It is an honour to be here being a Catholic."

Pope Francis criticised the lack of "infrastructures and basic services", including sewerage, electricity, good roads, school and hospitals.

"They are a consequence of new forms of colonialism ... countries are frequently pressured to adopt policies typical of the culture of waste," he said.

"This situation of indifference and hostility experienced by poor neighbourhoods is aggravated when violence spreads and criminal organisations, serving economic or political interests, use children and young people as 'cannon fodder' for their ruthless business affairs," he added, singling out the role women play in binding such societies together.

"I also appreciate the struggles of those women who fight heroically to protect their sons and daughters from these dangers."

Pope Francis has now arrived in Uganda where he will spend two days before continuing on to Central African Republic, a country wracked by sectarian conflict.

Security has been ratcheted up for the landmark visit over fears for his safety.

Islamist rebels have staged a string of attacks in Kenya, including the April massacre at Garissa university in which 148 people died, and the 2013 assault on the Westgate shopping mall that killed 67.

But the pontiff has shrugged off fears for his safety, joking that he was "more worried about the mosquitoes".

You have no doubt been hearing a lot about the Paris Agreement and know that it pertains to climate change, but are too embarrassed at this stage to ask for an overall explanation of what it's all about.